This invention relates generally to gas turbine engine control and more particularly to methods and apparatus for providing advance warning or avoidance of lean blow-outs.
Fuel and air are combined in a combustion process in gas turbine engines. To control the production of oxides of nitrogen (NOx) in this process, the combustion process is controlled by controlling flame temperature. Fuel and air can be premixed uniformly to avoid high combustion temperatures, and the engine can be operated below certain temperatures to avoid production of unacceptable amounts of NOx.
Gas turbines with dry low NOx combustion systems operate at very lean F/A (Fuel/Air) ratios closer to a Lean Blowout (LBO) boundary in order to maintain low NOx emissions. F/A ratios leaner than the LBO boundary value can result in partial or complete blowout of the flame. Further, can-to-can F/A ratio variability results in cans having F/A ratios closer to the LBO boundary that are more prone to blowout than cans that are operating at a larger margin from the LBO boundary. A blowout in one can sometimes leads to blowout in several adjacent cans, which can eventually trigger a turbine shutdown. Turbine trips due to LBO can be costly, and revenue can be lost during downtime and physical damage can be inflicted on the combustion components due to the blowout.